This invention relates to wireless/cellular radiotelephone systems and in particular to a method for self configuration, the autonomous assignment by the system of frequencies/channels to cells within the system, and a method for self calibration, the autonomous determination by the system of base station transmit power settings. Both rely on measurements collected by the system. In a particular illustrative embodiment, functionalities of the IS 136 Air Interface Standard MAHO/MACA are utilized to acquire the needed measurements. Specifically a self-configurable/calibratable wireless system utilizes an existing functionality of the cell site, specified by IS 136, to instruct its registered mobiles to measure received signal strength on specified channels in order to collect downlink signal strength measurements between mobiles and base stations.
The service area of a wireless communications system is partitioned into connected service domains known as cells, where radio telephone users communicate, via radio links, with the base station serving the cell. The base station (BS) is coupled to the land network. Efficient use of the available radio frequency spectrum is achieved through the reuse of the same radio frequencies in designated co-user cells that are sufficiently separated by distance so that the combined interference generated by co-channel and neighbor-channel cells is below tolerable levels.
Historically, the assignment of radio frequencies (or channels) to cells has been based on regularity assumptions (i.e., equal-sized regularly-spaced cells with uniformly distributed traffic loads), which enable the adoption of simple rules for identifying co-user cells, and for partitioning the RF spectrum into channel sets. However, because such regularity assumptions often do not hold, and thus the rules of regular channel assignment do not lead necessarily to the efficient utilization of the RF spectrum, a channel assignment approach, known as non-regular channel assignment, has evolved for to address this deficiency. Both regular and non-regular channel assignment approaches can be classified as fixed channel assignment, which is characterized by a fixed relationship between cells and the channels serving them.
In contrast to fixed channel assignment methods, a new classification has been developed known as flexible channel assignment. Such flexible channel assignment methods, exploit the capability of a system for remote, software-driven, returning of the base station radios, which capability enables channel capacity to adapt to traffic variation.
Wireless systems are generally migrating toward digital technologies from traditional analog wireless systems, although it is expected that analog systems will continue to serve a significant population of users for some time yet. In the digital environment, three candidates are emerging: Time-Division Multiple Access (xe2x80x9cTDMAxe2x80x9d), Global System for Mobile (GSM), and Code-Division Multiple Access (xe2x80x9cCDMAxe2x80x9d). The first two involve narrow-band channels that can carry, in separate time slots, three or eight conversations each, respectively. The latter uses wider channels that accommodate many users at once and can be re-used in abutting cells. From a service provider""s perspective, one of the fundamental differences between the two technologies is the need for channel assignment in the former, a requirement that is absent in the latter. As is apparent from the following discussion, channel assignment is very much a requirement for the analog systems used today.
The channel assignment function, as carried out in the prior art, is characterized by both the need for advanced planning of such channel assignments and a requirement for considerable data gathering. Additionally, such traditional channel assignment planning tends to achieve sub-optimal traffic loading in the cells of a wireless system, as well as sub-optimal traffic throughput in such a system. Associated with the channel assignment is setting or calibration of cell base station RF transmit power.
A self-configurable wireless system is one in which data is collected and channels are assigned to cells autonomously. The collected data provides information needed for channel assignment. Such a system is disclosed in the parent application Ser. No. 08/634,713, filed Apr. 18, 1996.
In a wireless communication system embodying the principles of the invention, frequency/channel assignments to cells are self configured and RF transmit power levels are self calibrated by using data collected by the wireless system determined by system functionalities as part of the self-configuration process.
The data required for self configuration and self calibration consists of signal strength measurements between mobiles and base stations. The measurements can be made either on the uplink or the downlink. Software coordinates the data collection, RF power setting and channel assignment.
In one illustrative embodiment of the invention, the required data is supplied automatically from MAHO/MACA (i.e., Mobile Assisted Hand Off; Mobile Assisted Channel Assignment) functionalities of the IS 136 Air Interface Standard (AIS), thus making an IS 136 system capable of self configuration and self calibration without additional hardware.
Specifically the system is initially started with preliminary data. Signal strength measurements can thus be made to provide a collection of data that is adequate for the efficient execution of the self configuration and self calibration algorithms.